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Identification and characterization of the enzymatic activity of zeta-crystallin from guinea pig lens. A novel NADPH:quinone oxidoreductase.

Publication ,  Journal Article
Rao, PV; Krishna, CM; Zigler, JS
Published in: J Biol Chem
January 5, 1992

zeta-Crystallin is a major protein in the lens of certain mammals. In guinea pigs it comprises 10% of the total lens protein, and it has been shown that a mutation in the zeta-crystallin gene is associated with autosomal dominant congenital cataract. As with several other lens crystallins of limited phylogenetic distribution, zeta-crystallin has been characterized as an "enzyme/crystallin" based on its ability to reduce catalytically the electron acceptor 2,6-dichlorophenolindophenol. We report here that certain naturally occurring quinones are good substrates for the enzymatic activity of zeta-crystallin. Among the various quinones tested, the orthoquinones 1,2-naphthoquinone and 9,10-phenanthrenequinone were the best substrates whereas menadione, ubiquinone, 9,10-anthraquinone, vitamins K1 and K2 were inactive as substrates. This quinone reductase activity was NADPH specific and exhibited typical Michaelis-Menten kinetics. Activity was sensitive to heat and sulfhydryl reagents but was very stable on freezing. Dicumarol (Ki = 1.3 x 10(-5) M) and nitrofurantoin (Ki = 1.4 x 10(-5) M) inhibited the activity competitively with respect to the electron acceptor, quinone. NADPH protected the enzyme against inactivation caused by heat, N-ethylmaleimide, or H2O2. Electron paramagnetic resonance spectroscopy of the reaction products showed formation of a semiquinone radical. The enzyme activity was associated with O2 consumption, generation of O2- and H2O2, and reduction of ferricytochrome c. These properties indicate that the enzyme acts through a one-electron transfer process. The substrate specificity, reaction characteristics, and physicochemical properties of zeta-crystallin demonstrate that it is an active NADPH:quinone oxidoreductase distinct from quinone reductases described previously.

Duke Scholars

Published In

J Biol Chem

ISSN

0021-9258

Publication Date

January 5, 1992

Volume

267

Issue

1

Start / End Page

96 / 102

Location

United States

Related Subject Headings

  • Substrate Specificity
  • Spin Labels
  • Quinones
  • Quinone Reductases
  • Oxygen
  • Nitrofurantoin
  • Naphthoquinones
  • NADP
  • Lens, Crystalline
  • Kinetics
 

Published In

J Biol Chem

ISSN

0021-9258

Publication Date

January 5, 1992

Volume

267

Issue

1

Start / End Page

96 / 102

Location

United States

Related Subject Headings

  • Substrate Specificity
  • Spin Labels
  • Quinones
  • Quinone Reductases
  • Oxygen
  • Nitrofurantoin
  • Naphthoquinones
  • NADP
  • Lens, Crystalline
  • Kinetics